The environment and health atlas of England and Wales: how it was created and what it shows

A collection of maps, intended to show the geographic distributions of environmental factors and disease have been launched today by researchers at Imperial College London. Dr Anna Hansell explains how they were created and what it can tell us

The Small Area Health and Statistics Unit (SAHSU) has been researching risks to the health of the population from environmental factors for more than 25 years, with much of the research using routinely collected health and population data at a small area scale.

Launched today, the environment and health atlas of England and Wales is intended as a resource to help better understand the geographic distributions of environmental factors and disease, provides some of this accumulated information as interactive maps of health conditions and of selected environmental agents at a small-area level in England and Wales.

The health maps provide a baseline picture of long-term geographical variability of 14 conditions (nine cancers, three common causes of mortality and two reproductive outcomes) over a 25 year period at a small-area scale. They show relative risks for each health condition (risks relative to those of England and Wales as a whole) for areas, not risks for an individual. Risks are provided at ward level, there are 8,800 wards in England and Wales with an average population of 6,000 people.

Health data (mortality, births and population) were supplied by the Office of National Statistics (ONS) and the cancer incidence data were derived from statistics compiled by national cancer registries; by the ONS for England and by the Welsh Cancer Intelligence and Surveillance Unit (WCISU) for Wales.

We produced the environmental maps at the finest resolution available, but to obtain detailed environmental data, we had to use a wide variety of sources which included some specific projects carried out by SAHSU.

A map of air pollution - PM10. Photograph: Small Area Health Statistics Unit

Air pollution mapping was carried out for a project entitled ‘use of geographic information for assessment of human exposure to air pollution’.

Water chlorination disinfection by-products (DBPs) data and water supply zone boundaries for the maps were supplied by 12 water companies as part of a previous study investigating potential associations with birth outcomes.

The sunshine duration map was based on UK Meteorological Office data supplied by the Met Office, while the pesticides maps were created for the INTARESE project to assess the impact of agriculture on health, using data came from the Pesticide Usage Survey (PUS) which is carried out by the Food and Environment Research Agency (FERA).

A map of sunshine duration. Photograph: Small Area Health Statistics Unit

It is important to note that simple comparison of the maps of environmental agents with the health maps can’t be used to demonstrate a causal association. Any such hypothesis would need to be investigated with additional information. This might include estimating the actual dose of the environmental agent received by an individual, asking about individual factors such as smoking, medical condition, family history and occupation etc. and by conducting further statistical analysis.

What is different about the environment and health atlas?

At first sight, the format of these maps looks familiar – and this is on purpose as people access information more quickly from familiar formats. However, several things are different about the information underlying the maps:

The maps are at a much finer resolution than many currently available maps of specific health conditions or environmental agents – often these are at local authority or regional level information, or they look at ‘health’ more generally rather than separate diseases or conditions as here

The two-tone colour scale chosen helps the eye to more quickly identify spatial patterns above or below the average for England and Wales

Another difference is that the maps are adjusted for deprivation; many diseases are strongly linked to deprivation so without this adjustment many of the maps would be likely to show patterns of deprivation rather than disease

The maps have also undergone statistical smoothing to allow for chance fluctuations where there are small numbers of cases. Smoothing helps make sense of geographical patterns when outcomes are rare

By taking account of these factors, the maps in this atlas are better able to help identify underlying variations in disease risk that may potentially be due to environmental risk factors.

Also measures of statistical uncertainty are presented alongside all the health maps and – where possible and available – the environmental maps. This is important as all the risks presented are estimates.

What insights does the new atlas provide?

Some examples of geographical patterns in the atlas are:

Skin cancer risk is greatest in southwest England even though sunshine duration is highest in southeast England. This suggests that despite the slightly lower duration of sunshine in the southwest, people may be more exposed, which could trigger further research into behavioral differences between the areas to explain this variation

The highest risks for liver cancer are seen in the Merseyside area. Some of this may be due to differences in coding of liver cancer in this region, but it may also in part reflect higher prevalence of risk factors, such as hepatitis C infection – there is a known higher prevalence of hepatitis C in current or former injecting drug users in London and the North West. More work to help understand these geographical patterns in liver cancer is being conducted by researchers at Imperial College

The atlas doesn’t have separate versions for researchers and for the public, but aims to provide information that is accessible to anyone using it. To help do this, SAHSU have been working with Sense About Science over the last two years to develop the format and text so that the information is relevant not just to researchers, but also to policy makers and members of the public and as part of this development, the atlas has been tested out in five workshops with 28 potential users of the atlas.

Maps featured in the atlas have accompanying information to help with interpretation and understanding. A print version is published at the same time by Oxford University Press; this has additional maps, statistics and review of the literature summarising what is known about each condition and agent.

Dr Anna Hansell is the assistant director of the Small Area Health Statistics Unit (SAHSU) based at Imperial College London and a clinical senior lecturer at the MRC-PHE Centre for Environment and Health.